The present invention generally relates to optical data communications and more particularly to optical dispersion correction in transimpedance amplifiers.
Optical data networks provide tremendous amount of data from one point or points to another point or points. However, optical data traveling through long reaches of optical fiber often undergoes various types of distortion. In one instance, the duty-cycle of the data pulses changes. Distortion is also introduced by communication components such as Erbium Doped Fiber Amplifiers (EDFA) that boost optical signals. In particular, the EDFAs add more noise to a logical one level of an optical pulse. As such, an altered duty cycle and a noisier logical one level may lead to lower sensitivity in an optical link.
Switching threshold adjustments may be made to help counter optical distortion. One example of adjusting the switching threshold involves adjusting the DC switching threshold of a final output buffer in a transimpedance amplifier (TIA), namely after current to voltage conversion and subsequent amplification through gain stages. However, a large input signal into the TIA may drive the gain stages, following the I-to-V stage of the TIA, into saturation. Thus, any adjustment to the switching threshold would be performed on a saturated signal. This is generally not desired, since some of the equalization algorithms applied to the data downstream may require that the circuitry be operated in the linear range. Also, since the threshold adjustment may be performed on the output buffer, the TIA may have to be DC-coupled to the post-amplifier to make a threshold adjustment.